Science and Education Publishing American Journal of Medical Case Reports 2374-216X 4 7 2016 8 12 Nocardia arthritidis Infection in an Immunocompetent Human in the United States 251 254 EN Osamuyimen Igbinosa Section of Infectious Diseases, MedStar Washington Hospital Center, Washington DC USA Owen Igbinosa Krishna Dass Glenn Wortmann AJMCR20164710 10.12691/ajmcr-4-7-10 2016 4 14 2016 6 18 2016 8 10 Patients with T-cell defects are at the highest risk for nocardiosis, a potentially life-threatening infection caused by several species of the genus, Nocardia. We report a case of disseminated Nocardia arthritidis in a patient who had no recognizable risk factors for immunodeficiency. A 43-year-old woman was noted to have a left upper lobe cavitary lesion on an outpatient computerized tomography (CT) scan that was performed for evaluation of pelvic congestion syndrome. She subsequently had an image-guided biopsy of the lesion, but the results were still pending when she presented at the emergency department with a transient episode of aphasia. A CT scan of the patient's head revealed hypodensities in the right frontoparietal and left frontal lobes. A modified acid-fast stain on the lung biopsy specimen demonstrated variable, branching, filamentous bacteria with morphology consistent with Nocardia species. Matrix-Assisted Laser Desorption / Ionization - Time-of-Flight (MALDI-TOF) Mass Spectrometry at a reference laboratory later identified the bacteria as Nocardia arthritidis. This case highlights that disseminated nocardiosis can occur in an apparently healthy population. A more detailed immunologic evaluation that include screening for chronic granulomatous disease, anticytokine autoantibody deficiency and interleukin-12-gamma interferon pathway deficiency may further assist in the diagnosis of patients' underlying diseases.